The present disclosure relates to a display unit and a method for fabricating the display unit. More particularly, the invention relates to a display unit in which organic electroluminescent devices that emit light of different colors are arrayed, the organic electroluminescent devices including luminescent layers, the thickness of which varies according to color.
Organic electroluminescent devices using electroluminescence of organic materials have been receiving attention as light-emitting devices capable of achieving high-luminance light emission at low-voltage DC drive, each organic electroluminescent device including an organic layer portion in which a hole-transport layer and a luminescent layer are disposed, the organic layer portion being provided between a lower electrode and an upper electrode. In a full color display unit including such organic electroluminescent devices, organic electroluminescent devices each emitting light of red (R), green (G), or blue (B) are arrayed on a substrate.
In such a display unit, a luminescent layer composed of at least a luminescent material of the corresponding color is formed by patterning for each device. Furthermore, by designing the devices, each emitting light of R, G, or B, to have a resonator structure in which only emitted light of the corresponding color is resonated and extracted, it is possible to improve the color purity of emitted light extracted from each device, and to increase the extraction efficiency of emitted light. In such an organic electroluminescent device, for example, an anode which also acts as a mirror, an organic layer which includes a luminescent layer, and a cathode which also acts as a half mirror, are disposed in that order. By setting the distance between the anode (mirror) and the cathode (half mirror) so as to be equal to the optical distance that allows light with a light-emitting wavelength of the corresponding color to resonate, only the characteristic wavelength in the emitted light generated in the luminescent layer is extracted from the cathode (half mirror) side.
When a display unit is fabricated using the organic electroluminescent devices of the individual colors having such a resonator structure, by adjusting the optical distance in each device only by the thickness of the luminescent layer, the other layers can be commonly used, and thus the fabrication process can be significantly simplified.
As a method for forming the luminescent layer by patterning, a thermal transfer method has been proposed. When the thermal transfer method is used, a display unit is fabricated, for example, as follows. First, an anode is formed on a substrate (hereinafter referred to as the “device substrate”) of the display unit. In addition, a luminescent layer is formed on another substrate (hereinafter referred to as the “transfer substrate”) with a light-absorption layer therebetween. The device substrate and the transfer substrate are placed such that the luminescent layer and the anode face each other, and the luminescent layer is thermally transferred onto the anode of the device substrate by irradiating the transfer substrate with laser light. At this stage, by performing scanning using spot irradiation of laser light, the luminescent layer is transferred only onto a predetermined region on the anode with high positional accuracy.
With respect to the use of the thermal transfer method, a method has been proposed in which a hole-transport layer is further formed on a light-absorbing layer of a transfer substrate with a luminescent layer therebetween, and then irradiation of sufficient light (laser light) is performed so that transfer is performed with the hole-transporting material being mixed into the luminescent material. By using such a method, the efficiency and stability of the organic electroluminescent device (OLED) are reported to be increased. (Refer to Japanese Unexamined Patent Application Publication No. 2004-71551, in particular, columns 8 to 10.)